My style changes all the time. I like clothes. And I think it's OK to think about clothes just so long as you also think about other things. I'm not interested in clothes to the point where they'll push other things out of my mind, I just see them as a way of expressing yourself, and a pleasure, really. I happen to be in a line of work where I get given lots of clothes, and I definitely think it's fun, but I know that ultimately fashion is not that important. I use fashion though, as a way of thinking about who I am. I hold something up against my body and ask myself, 'Can I wear this?' If it doesn't feel like 'me', then I suppose I ask myself why.

I was always dressing up as a kid. I had a dress for all the Los Angeles bar and bat mitzvahs that I was going to when I was 13 which I was crazy for. It was green, dark, shimmery. Very 1980s. It was slightly off-the-shoulder, which I thought was very sophisticated. And it made me feel great. Boys weren't a huge part of my thoughts right then, but the dress made me feel hot.

When I was in grade school in LA I really loved Cyndi Lauper. I did everything I could to look like her. I had wild outfits, and always wore different coloured socks. I wore loads of ribbons in my hair, and let them fall in my eyes. My parents would let me dress however I wanted to, but at school I got a few funny looks. I guess when you're a kid, if you're dressing yourself, people have to allow for a certain element of wackiness. I went to one school where I had to wear a uniform, but we did everything we could to look different, stretching the rules to the limits to push the uniform. I admired the older girls who wore pink tights under their uniforms, and kept their skirts really short. I'd get about one demerit a year for breaking the uniform rules, but it was worth it, a badge of pride. These days, instead of Cyndi, I admire Charlotte Gainsbourg, and Julie Christie in her old films. The way they dress just looks so sexy.

As an actress you can feel totally comfortable in someone else's clothes. In Sherrybaby for instance, I felt comfortable in something that I would never consider wearing in my real life. Wardrobe is a big part of getting into a character for me. But how much actors get to input depends on the movie. On a big studio movie like World Trade Center, which was directed by Oliver Stone, I wasn't really asked what I felt about the clothes I was wearing, apart from on a courtesy level, but there are a whole bunch of people standing around trying to monitor which shades of skirt look better with the set, and which colour goes with the film stock. That kind of thing is very difficult for me, because I couldn't feed into it. But on Sherrybaby I had a huge amount of input. I wanted to use her wardrobe to show that you don't have to stop being hot just because you're a mother.

When I was pregnant my friends were very strict with me about clothes. They wouldn't let me wear anything that wasn't 'embracing my sexuality'. I tried, but it's a lot of work being a mum! I went to Paris when my daughter was tiny and bought lots of beautiful clothes, but I didn't wear a single thing. I just stayed in baggy T-shirts. Filthy baggy T-shirts. It's totally possible to be a sexy mum, but it's a lot easier to just be comfortable in your baggy filth.

I avoided seeing any of my Agent Provocateur campaigns on billboards. But I did the campaign because when my daughter was tiny a friend introduced me to their maternity bras. I bought a hot-pink one with matching underwear. It made me feel great. So I felt like I owed them. Also, I thought it would be fun, and funny too. A little bit ironic. Then suddenly I'm in front of the camera in my underwear saying, 'Umm, how did I get here?' But I'm very proud of the pictures. To be honest, it was all kind of ... wild.